1. Field of the Invention
The present invention relates to an electromechanical robotic device that is worn over the human arm.
In particular, this invention relates to a torso-mounted, powered arm exoskeleton that is capable of moving in parallel with the human arm, reacting and exerting forces, and providing sensory feedback during shoulder rehabilitation.
2. Description of the Related Art
Robotic arm exoskeletons are powered electromechanical devices that surround the arm and interface the human limbs via mechanical attachments or inflatable bladders. The base member of an arm exoskeleton is either mounted to the subject via a torso support worn on the upper extremity or to a ground support such as a floor or wall. The former will henceforth be referred to as “torso-mounted” and the latter as “floor-mounted”.
The joints are powered with actuators either by direct-drive or a mechanical transmission such as a gear, cable-tendon, belt, or lever arm. Floor-mounted exoskeletons typically use cable-tendons to drive the joints from motors located in the base in order to off-load weight from the arm.
To be used for shoulder rehabilitation, an arm exoskeleton should possess the following properties: (1) anthropomorphic arm motion, (2) singularity-free shoulder workspace, and (3) shoulder axes intersect at the anatomical glenohumeral (GH) joint.
To realize anthropomorphic arm motion, the joint ranges must be comparable to those of the human arm. Matching the joint ranges is exceedingly difficult when using single-axis revolute joints because the linkages easily interfere with each other thus limiting the range of motion. By skewing the third joint axis away from being co-linear with the upper arm, the exoskeleton shoulder (rotation) workspace more closely matches that of the human shoulder. To keep the joints aligned with those of the human, the lengths of the upper arm and forearm linkages should be adjustable to match the anatomical limb lengths. This adjustability is usually absent when the joints are driven with cables from motors mounted in a base platform.
To achieve a singularity-free shoulder workspace, no two of the three shoulder joints can become aligned while operating within the human range. In this configuration, the shoulder is “gimbal-locked” and can only rotate about two independent axes. For an orthogonal three-axis shoulder assembly, this configuration occurs when the first and third joint axes align so that the singularity is along the first joint axis. By skewing the first joint axis medially (downward toward the torso) in the frontal plane, the singularity is no longer straight up down along the shoulder azimuth but rather inward toward the body which is not reachable by the human arm.
To maintain coincidence of the exoskeleton shoulder joint with the human glenohumeral joint, the shoulder joint must be able to translate approximately along the surface of a sphere relative to the scapula joint when lifting the arm above shoulder level. This torso-to-shoulder articulation is required to provide anatomically correct shoulder movement and avoid misalignment stress during elevation of the upper arm.
Although it is not a requirement, a torso-mounted design is highly preferable to allow subject mobility and energy transfer from the trunk to the arm during functional rehabilitation. A torso-mounted design also provides a deterministic relationship between the trunk and the arm through mechanical articulation of the exoskeleton. In floor-mounted exoskeletons, the posture of the human torso is left unconstrained, and the exoskeleton configuration with respect to the torso cannot be determined without external instrumentation.
Most arm exoskeletons built to-date were developed as force-feedback devices for tele-operation or virtual reality (VR) applications. The purpose of these exoskeletons is to impart “contact” forces at the handgrip of the exoskeleton that replicate forces sensed by the slave arm during tele-operation or interaction with a virtual environment in VR applications. These types of exoskeletons are typically not capable of exerting enough force for exercise therapy or having the interfaces required to apply force at multiple contact points along the length of the arm. Many kinematic properties required for shoulder therapy, such as anthropomorphic range of motion and torso-to-shoulder articulation, are often lacking as well.
Before the present invention was undertaken, we performed an extensive search of the prior art (Carignan et al., 2005). The following exoskeletons were built as force-reflecting master arms and haptic devices:
Sarcos, Inc. produced a hydraulic-powered master arm, which had a three-axis intersecting shoulder joint with a skewed first axis in the frontal plane and a third joint axis co-linear with the upper arm. The design was floor-mounted, and it had no torso-to-shoulder articulation (Jacobsen et al., 1991).
Odetics, Inc. built the FreFlex master arm, which had only two shoulder joints. It was floor-mounted and had no torso-to-shoulder articulation (Williams et al., 1998).
U.S. Pat. No. 5,845,540 (Rosheim) discloses a master arm exoskeleton structure with a three-axis intersecting shoulder joint, which does not intersect at the GH joint. The exoskeleton is torso-mounted but does not have torso-to-shoulder articulation.
Exos, Inc. built the Exos Force ArmMaster, which has a three-axis intersecting shoulder joint. The first shoulder joint axis is skewed at an acute angle to the azimuth axis in the sagittal (not frontal) plane, and the third shoulder joint axis is co-linear with the upper arm. The exoskeleton is torso-mounted, but it has no torso-to-shoulder articulation (NASA Tech, 2004).
The PERCRO Lab produced the GLAD-IN-ART Exoskeleton, which has a three-axis intersecting shoulder joint and co-linear third joint axis. It is floor-mounted and has no torso-to-shoulder articulation (Bergamasco et al., 1994).
The University of Tokyo produced the Sensor Arm, which has a three-axis intersecting shoulder joint and co-linear third joint axis. It is floor-mounted and has no torso-to-shoulder articulation (Nakai et al., 1997).
The Korea Institute of Science and Technology built a torso-mounted master device described in U.S. Pat. No. 6,301,526 (Kim, Lee & Lee), which has a three-axis intersecting shoulder joint. However, the shoulder joint does not intersect at the anatomical GH joint, and it has no torso-to-shoulder articulation.
Beijing University produced a torso-mounted arm exoskeleton device with a three-axis intersecting shoulder joint and co-linear third joint axis. It is driven by flex-cables from motors in a backpack, but it does not have torso-to-shoulder articulation (Chou et al., 2004).
Note that several labs have also built passive (unpowered) exoskeletons for various purposes, but these cannot exert forces required for physical therapy. However, we note them here for their kinematic properties:
MB Associates built the passive MB Exoskeleton with adjustable link lengths for taking anthropomorphic measurements. It has a three-axis intersecting shoulder joint with a co-linear third joint axis. It is torso-mounted, but it has not torso-to-shoulder articulation (Repperger et al., 1991).
The University of Salford built the passive Salford ArmMaster for placing tactile sensors on the arm, which has a three-axis intersecting shoulder joint and co-linear third shoulder joint axis. It is torso-mounted and has torso-to-shoulder articulation (scapula tilt and medial rotation). It did not have structural support for exerting significant joint torques (Caldwell et al., 1998)
The development of robotic exoskeletons for physical therapy is relatively recent. Here is a summary of rehabilitation arm exoskeletons that we know of which have been developed to-date:
The University of Newcastle built the Motorized Upper Limb Orthotic System (MULOS), which is a wheelchair-mounted exoskeleton developed to assist persons with weak upper limbs. It has a three-axis intersecting shoulder joint, and the first shoulder joint is tilted at an acute angle to the shoulder azimuth in the sagittal (not frontal) plane. The third joint axis is skewed with respect to the upper arm to increase workspace. The link lengths are fixed and there is no torso-to-shoulder articulation. It not powerful enough to be used for physical therapy (Johnson, 2001).
Arizona State University built the Robotic Upper Extremity Repetitive Therapy (RUPERT), which is a torso-mounted exoskeleton with three total joints (only one shoulder) powered using pneumatic muscles. It does not have torso-to-shoulder articulation (He et al, 2005).
U.S. patent application Ser. No. 10/017,280 (Zemlyakov & McDonough) discloses an upper extremity exoskeleton structure that has a three-axis intersecting shoulder joint and two torso-to-shoulder articulations. The first torso-to-shoulder joint is rotation about the torso azimuth, which produces shoulder protraction-retraction. The second torso-to-shoulder joint is rotation about an axis perpendicular to the frontal plane, which produces shoulder elevation-depression. These axes intersect at a fixed-point midway between the center of the shoulder joints (with a co-linear upper arm joint), and not at the center of rotation of the scapula. In addition, the first shoulder joint axis is parallel to the torso azimuth axis, which produces a singularity when the upper arm is horizontal thereby limiting its usable workspace. The exoskeleton is floor-mounted and driven by cables from motors mounted in the base platform.
L-EXOS built by PERCRO Lab (U.S. patent application Ser. No. 10/540,918 Bergamasco et al.; Frisoli et al., 2005), Exoskeleton Prototype III built by the University of Washington (Rosen, 2005), and ARMOR built by Seibersdort-Research (Mayr et al., 2006) are all floor-mounted exoskeletons with a three-axis intersecting shoulder joint and a co-linear third joint. They utilize cable-tendons to drive the joints from motors in the base platform, and they have no torso-to-shoulder articulation.
We have encountered only two powered rehabilitation exoskeleton designs that incorporate torso-to-shoulder articulation:
ETH Zurich built ARMin II, which is a floor-mounted design with six revolute joints that allow three-axis shoulder rotation (third joint co-linear with upper arm), elbow flexion/extension, pro/supination of the lower arm, and wrist flexion/extension (Nef et al., 2006). A seventh linear joint is coupled to shoulder flexion movements to enable the shoulder axis triad to move in vertical direction when the arm is lifted. Although this vertical motion is approximately correct, it is not along an arc traveled by the anatomical shoulder joint.
U.S. patent application Ser. No. 10/443,111 (Schiele & Visentin) discloses the ESA Human Arm Exoskeleton, which is a torso-mounted exoskeleton with a total of six joints for realizing rotation and translation of the shoulder joint: two rotations in the torso assembly, three rotations in the shoulder assembly, and one prismatic joint connecting the two assemblies. While this design allows full torso-to-shoulder articulation, the prismatic joint and several of the rotational joints in the shoulder complex are passive (spring-loaded) and thus cannot be actively controlled. In addition, the three rotational joints in the shoulder assembly do not intersect at the GH joint (Schiele & Visentin, 2006).
To summarize, many existing exoskeletons have design features relevant to proper shoulder articulation for rehabilitation, but none have the same portability, anthropomorphic range, and powered kinematic sequence as the present invention: torso-to-shoulder articulation to enable scapula rotation (shoulder elevation) followed by a tri-axial shoulder joint to allow three-axis rotation of the shoulder about the anatomical glenohumeral joint.